Ted Cruz and Marco Rubio aren’t only taking their campaigns onward to South Carolina. While the next Republican primary commands the public’s attention, both are also running for president by mounting quiet symbolic protests at American embassies around the world.

A single senator has nearly unilateral ability to block any confirmation, whether he’s in the Capitol or on the hustings hundreds of miles away. The junior senators from Texas and Florida are using their power to place indefinite “holds” on diplomatic nominees, hoping to highlight their own foreign policies and their condemnations of President Barack Obama’s conduct of international affairs. Both campaign rivals have been pursuing the tactic since last year, yet another way they’re using similar approaches to advance their White House quests while leading their Senate lives. (Voting alike far more often than not during their three years together in Congress is the most obvious example of that.)

Rubio has focused his ire on a single would-be ambassador, Roberta Jacobson, nominated last spring to become envoy to Mexico after three decades working on Latin America in both Democratic and Republican administrations. Her disqualifying sin, in Rubio’s view, has been leading negotiations on the recent diplomatic, commercial and travel rapprochements with Cuba as an assistant secretary of state.

Cruz, as is his wont, has launched a more sweeping and dramatic effort. He has a blanket hold on all eight pending ambassadorial nominees considered “political,” meaning they come from outside the career foreign service. His initial aim was to build leverage for blocking the nuclear agreement with Iran. Since that didn’t work, the obstruction has been labeled a protest against both the six-nation deal with Tehran and Obama’s overall approach to world affairs.

The standoff has come only briefly into view a few times before this week. On Monday, Democrat Amy Klobuchar of Minnesota went to the Senate floor and announced that, until Cruz relents, she would make a parliamentary move almost every day seeking roll call votes for filling the two long-vacant embassies in Scandinavia.

(There’s some parochial motive to her cherry-picking approach. More Norwegians live in her state than anywhere else but Norway, and the nominee for Oslo is Minneapolis lawyer and human rights activist Sam Heins, who raised more than $1 million for Obama’s re-election. Klobuchar also has thousands of constituents with Swedish heritage; the nominee for Stockholm is another Obama fundraising bundler, retired California investment banker Azita Raji.)

“How can one senator stand in the way of a vote affecting relations that are 200 years old?” Klobuchar asked. “Our economic partnership with these countries is enormous.”

With Cruz off campaigning, it has fallen to Majority Leader Mitch McConnell to block her unanimous consent requests in deference to his fellow Republican. Doing otherwise would weaken intra-party loyalties and prove self-defeating, because the angry senator could gum up the works other ways. Floor leaders learned that the hard way in the 1980s and 1990s when they tried to work around Sen. Jesse Helms of North Carolina, a forefather of today’s combative GOP conservatives, who pioneered the practice of putting holds on ambassadorial nominations by presidents of both parties to pressure the State Department to adopt policies more to his liking.

In no case are Cruz and Rubio alleging the nominees are under-qualified for their posts. And all the pending political picks have won unchallenged endorsement by the Foreign Relations Committee or have been confirmed to another diplomatic job in recent years. The other five are David McKean, a State Department official who held senior staff jobs on the Hill for two decades, for Luxembourg; Cassandra Butts, Obama’s first-term deputy White House counsel, for the Bahamas; Laura Holgate, a nuclear weapons expert at the National Security Council, for the United Nations disarmament agency in Vienna; John Estrada, a Marine sergeant major who vouched for Obama’s commitment to national defense in 2008, to return to his native Trinidad; and Mari Carmen Aponte, who would move from the embassy in San Salvador to the Organization of American States.

The roster of would-be ambassadors, in other words, has already been culled of almost all the Obama nominees who infuriated Senate Republicans (and career diplomats) for having political connections and campaign generosity inversely proportionate to their government or in-country experience.

To be sure, every president for at least the past century has been chided for rewarding too many buddies and benefactors with cushy overseas postings, even after a 1980 law explicitly ruled out campaign giving as a qualification for a diplomatic job. And over time, more ambassadorial nominees have been opposed for being “political hacks” than for -- as in the current Cruz and Rubio scenarios -- embodying foreign policies objectionable to a single senator.

Democrats pushed several big Obama donors through the Senate before handing over the keys at the end of 2014. Most of those left hanging then withdrew their nominations – most famously George Tsunis, a hotel magnate and Obama mega-donor from Long Island who revealed a comprehensive ignorance about Norway during his confirmation hearing to become ambassador there.

Facing a Senate GOP majority during his lame-duck years, however, Obama has adapted to political reality and as a result all but one of the 43 ambassadors nominated and confirmed in the past 14 months have made their careers in federal service. (The sole exception was Fitz Haney, a businessman with expertise in Latin America and a modest Obama bundler whom the Senate dispatched to Costa Rica last June.)

At the moment, 32 percent of all Obama’s envoy nominees have been political people, the highest since Ronald Reagan’s 38 percent. If Cruz and Rubio persist in their holds, and only foreign service veterans get through this year, the share will drop closer those of other recent presidents.

And then, if one of those GOP senators wins the White House, there’s no doubt but that their initial rosters of would-be ambassadors will come under witheringly intense scrutiny from the Democrats.